1. Field of the Invention
This invention relates, generally, to dowel pins, and more specifically relates to an improved dowel pin that has application in the dental crown and bridge making industry.
2. Description of the Prior Art
Dowel pins are widely used in the industry that makes dental crowns and bridges and, of course, in many other industries and applications as well. The conventional pin of the type used when making dental crowns and bridges has a body or stem portion and a head portion, the latter portion essentially comprising a knurled rod-like member of uniform transverse cross section and the former portion comprising a uniformly tapered member, the cross section of which progressively increases from its free end to the point where such body portion abuts the knurled head portion.
When a dental crown or bridge is being made, a base of plaster is cast to serve as a mount upon which the models of teeth or artificial teeth are mounted. The body portion, or stem, of the respective dowel pins are positioned before the plaster is poured into the mold so that a perfect fit will be formed between the stem and the base. The artificial tooth is then bored to receive the knurled portion of the pin and the knurled portion is cemented into place. (The knurled portion may also be positioned by the pouring procedure as well). It is necessary to remove the stem portion of the pin from the base during the construction process, and it is critical that the pin be re-seated into its pre-retraction position in order to ensure a good fit when the crown/bridge is worn by the patient.
The circular transverse cross section of the stem portion of conventional pins introduces error into the bridge construction procedure because such circular stems will rotate within their respective cavities. Moreover, since conventional dowel pins are of one length, from time to time a small tooth is encountered which will not receive a conventional pin in its entirety. When this occurs, the knurled portion of the pin will protrude through the tooth and the protruding portion must be laboriously trimmed off. Alternatively, the lab technician may select a smaller pin. Thus, different sizes of pins must be kept on hand.
The knurl is provided on conventional pins in the hope that such knurl will serve to guard against separation of the tooth from the pin. In practice, however, the traction between tooth and knurl is often too little, and teeth will often separate from their respective pins when the tooth is removed from the plaster base. Moreover, the knurled portion of a conventional pin often does not fit properly in its bore if the drill that bores the hole in the tooth is worn. A worn drill will make a tapered bore which does not adequately receive the knurled portion of the pin.
Further, the uniformly tapered stem portion of a conventional dowel pin results in a pin that is difficult to grasp. The lab technician must securely grasp the pin during the construction process. The dentist will also need to grasp the tapered portion of the pin when making the final fitting of the crown to the patient's natural tooth. When such a final fitting is being performed, the model tooth-capped with the crown-is pulled out of the mold and serves as a holder or nest for the crown. The crown is worked on, then separated from the model tooth and fitted onto the patient's natural tooth.
There is a need in the industry for an improved dowel pin, but the needed pin does not appear in the prior art.